These are the colours that I use up the fastest.
Burnt Sienna is a colour I use frequently to mix with French Ultramarine to produce grays. Most brands use PBr 7 as their Burnt Sienna but Winsor & Newton's version uses PR101. WN's version looks warmer while Daniel Smith's version is cooler. When mixed with French Ultramarine, DS's version looks cooler.
I usually use this mix to paint dark clouds, tree trunks, anything that's gray and glaze over shadow areas.
Sap Green is another one of my favourite colours. You can use it straight from the tube onto paper and it won't look out of place.
To add variation to the green, I would always add French Ultramarine to create the colour blending and with Burnt Sienna to make the greens even darker, for the shadow areas.
There's a lot of green in nature so it's a colour that I use quite often.
New Gamboge is also a really convenient and versatile colour. It's such a lovely warm yellow that's so close to orange. You just have to add a bit of red to it and you can get a vibrant orange. You can also use it on its own to paint subjects that are yellow. Sometimes I would mix this with Lemon Yellow to get some variations in the yellow.
The old formula for Sap Green is PO49 (Quin Deep Gold) and PG7 (Phthalo Green). The new formula now is PO 48, PY 150, PG 7. Daniel Smith is now using a new formula because they have ran out of Quinacridone Deep Gold.
New Gamboge is also using a new formula. PY 97, PY 110 is now used instead of the original PY153. .
I'll be getting the colours with the new formulas to test them out while I still have some of the old formula left.